Meter drag magnet



March 17, 1925.

w. H. PRATT METER DRAG MAGNET Ff iled Aug. 11, 1922 Patented Mar- UNITED STATES WILLLAI -11. PRATT,

PATENT; oFIHcE.

ELECTRIC man nnao MAGNET.

application filed August 11, 1922. Serial no. 581,181.

To all whom it may come 1%.

- Be-E'i known-that I, WILIJAM H. PRATI,

a citiien of the. United States, residing at Lynn, county of Essex, State of'Massachusetts, have invented certain new and usefullmprovements in Meter Drag Magnets, of which the following; is a specificati0n.- V

My invention relates to meter magnets and more particularly to the structure of damping magnets for induction type meters.

It has long beenthe practice to construct meter damping magnetsintheform of one or more C-shaped pieces of permanent magnet steel. The opening in the C constitutes the air .gap thru which the meter disc of conducting material rotates to produce a dampin efiect in a well understood manner.

e damping magnet as thus constructed aifords no practicable metho d of accurately cutting or adjusting the air Qne objectof my iIIVGIIfiOD'lS to provi a damping magnet of such structure that theair ga may be readily and accurately cut and adjusted.

It is sometimes an advantage to have different portions of. a 'dampmg magnet made of material of relatively different coercivity, an advantage which cannot be obtained where the magnet is made of a single piece of material. Another object of my invention is to provide a damping magnet made up of separate ortions of ma rial having the esired magnetic coercivity.

y The features'of my inventionwhich I believe to be novel and patentable be pointed out in the' claims appended here= to; r The manner of carr g my invention into efiect and the details of construction of a magnet built in accordance with my invention will now 'be'expl'ained in connection with the--aocompanying..d1 in .i

which Fig. 1 illustrates the structure of a magnet built in accordance with .my invention; Fi 2 is a cross section taken on line A-A 0 Fig. 1; and Fig. 3 shows a further modification of my invention.

Inprevious types of damping magnets it will be evident that in order to grind the air gap in which the meter disc is torotate, use must'be made of very thin grinding wheels. Thin .wheels are expensive to use as their breakage is high and thework of grinding must be carried on at a slow rate. Furthermore, it is difli:

gnetic mate cult to obtain an accurate definite air gapwhere" the space available for machining is so small.

In order to overcome thisobje'ction I provide a magnet structure divided into sections each of which may be groundwith robust grinding wheels and thereafter assembled to obtain an accurate definite air grinding or 'gap. Referring to Figs. 1 and 2, I show andto the magnet shelf or support 4.- by

screws 6 and washer 7. The strap 5 is provided with a groove 8 into whichpfitsahead 9 provided .on section 1 as shown in Figs. .1 and 2. Section 2*togetlier with strap 5 may be removedby sliding said parts relative to section 1 until ove 8 7 is disengaged from bead 9. Atightening of screws 6 clamps'thetwo sections to the support 4. er appropriate fastening means I may be .ptrovided instead of the structure shown. Should it become necessary to grind the surfaces 'an' excessive amount to make them even, thereby making the air gap too great, the air gap may be corrected b placing shims between the surfaces 3 e shims, if such are necessary, and likewise the strap 5 may be made of magnetic material such as mild steel. or one may be made of magneticmaterial and the other of brass. The strength of the magnetic field across the air adjusted to some extent in this manner.

" It will be noticed that the length of-the magnetic paths be ween oppodtew oles in the two sections l and 2 are considerably difi'erent and therefore it will be an advan- 100 tage to make netic coercivi'ty; than section 1. To this end the section 2 of a higher mag- I find it desirable to use ordinary magnetic steel for section'l and cobalt steel for section 2. It is possible to adjust the damping 105 effect produced by interchanging section 2 for another section of similar dimensions having netism.

In Fig. 3 have shown another modifica- 0 gap may be a greater or smaller permanent magtion of my invention where the double damping magnet is made of three pleces,

consisting of a section 1 similar to that shown in Fig. 1, and two removable straight sections 10 andll. The sections 10 and 11 are preferably secured to the section 1 by screws 12 and these sections may, if desired,

be made adjustable toward and away from Wpolaritybf t l 1e.permanent magnet sections are indicated by the letters N and S. While I have shown the structure in Fig. 3 asa double magnet, each C-shaped section may be made separate.

In accordance with the provisidns of the patent statutes, I have described what I now consider to represent the best embodiment of'my invention but I desire to have it understood that the structures shown are only illustrative and that the invention may be carried out by other modifications thereof.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A drag magnet for meters comprising" a C shaped permanerit-magnet section of cobalt steel. and a relatively longer perindnent magnet section of ordinary magnet steel bent to a shape to enclose the C- 'shaped section so that the north and the south ends of one section form narrow air gap's with the south and north ends respectively of the other section, and means for securing said sections together.

2; A drag magnet for meters comprising a C-shaped permanent magnet section and a relatiyely longer permanent magnet section of lower coercivity than the first men tioned section bent to a shape to enclose the C-shaped section so that the north and south ends of one section form narrowvair gaps with the soutlrand-north ends respectively of the other section and means for securing said sections together.

3. A damping magnet for electric meters comprising a plurality of permanent magnet sections, said sections having different degrees of magnetic coercivity.

LA magnetic structure made up of two sections of permanent magnetic material forming a drag magnet, one section having a shorter continuous magnetic pathand 'nrade of material having a greater degree of ,magnetic coercivity than said other section.

Inwitness whereof, I have hereunto set my hand this 9th day of August 1922.

WILLIAM PRATT. 

